a) Field of the Invention
The invention relates to a method for the production of a steering spindle part, which forms a section of a steering spindle for a motor vehicle and is implemented in the form of a hollow shaft. The steering spindle part comprises, at least adjoining one of its ends, a connection section having at least over a portion of its length a greater wall thickness compared to a section of the steering spindle part adjoining the connection section. For the production of the steering spindle part, an initially hollow-cylindrical tube which, at least section-wise, is reshaped is utilized as the starting product. The invention further relates to a steering spindle for a motor vehicle with at least one steering spindle part forming a section of a steering spindle for a motor vehicle and implemented in the form of a hollow shaft and which, adjoining at least one of its ends, comprises a connection section which, at least over a portion of its length, has a greater wall thickness compared to a section of the steering spindle part adjoining the connection section, wherein the steering spindle part includes a tube extending over its length.
b) Description of Related Prior Art
Steering spindles of motor vehicles conventionally comprise several steering spindle parts, each of which forms a section of the steering spindle. The steering wheel is secured in place on the rear end of the steering spindle section, which with respect to the traveling direction is the rearmost. On the steering spindle section, which with respect to the traveling direction is the foremost, a pinion gear is frequently secured on its front end for the meshing into the steering gearing. Apart from steering spindle parts connected with one another via universal joints, steering spindle parts displaceable (telescopable) with respect to one another are provided, which serve for the purpose of setting the length of the steering column and/or for absorbing longitudinal displacements in the event of a crash.
The connection of the steering wheel with the rearmost steering spindle part in a known embodiment takes place by means of a threaded joint. The steering spindle part implemented in the form of a hollow shaft exhibits for this purpose at its end a connection section which, starting from the end of the steering spindle part, comprises a substantially hollow-cylindrical section and adjoining the latter a conical section which widens toward the middle of the steering spindle part. The hollow-cylindrical section is provided with inner threading and outer toothing. The outer toothing meshes into an inner toothing of the hub of the steering wheel and the threaded joint of the steering wheel on the steering spindle part is accomplished by means of the inner threading. The steering spindle part must herein have a wall thickness of adequate size in the connection section, in particular in the hollow-cylindrical end section. This wall thickness is greater than the wall thickness required for the transfer of the torque over the remaining length of the steering spindle part. For the implementation of the steering spindle parts therefore tubes are conventionally utilized which initially have a greater wall thickness, apart from the connection section, than is required. Subsequently working, in particular hammering or a like reshaping method, for example ductile-working, of the tube over its entire longitudinal dimension takes place. In the connection section the diameter of the tube is decreased herein. Furthermore, structures can also be worked over sections into the tube, which structures serve, for example, for the telescopable, yet nonrotatable, connection with a further steering spindle part. The implementation of such contours, in particular in the form of arcuate toothings or cloverleaf profiles, is known. DE 197 50 005 C1, for example, shows steering spindle parts with such contours.
Due to the required reshaping of the tube over its entire length, this process is highly labor-intensive and also difficult to control.
While it is possible to increase the wall thickness of a tube by hammeringdue to the factors imitating such thickening, a tube must nevertheless be employed as the starting product which has a greater wall thickness than would be necessary for the required torque transfer. The steering spindle part becomes thereby overall heavy or the tube must again be worked over its entire length in order to appropriately decrease the wall thickness, apart from the connection section.
DE 10 2004 009 188 A1 discloses two telescopably connected steering spindle parts which, viewed in longitudinal section, have complicated contours with different thickness regions of their wall thicknesses. At their remote ends, connection sections are provided for the connection with a steering wheel or a steering gearing, respectively.
Securing a steering wheel on a steering shaft by means of a bolt disposed transversely to the axis of the steering spindle, which bolt cooperates with a holding cone and shifts it into a recess of the steering wheel hub and tightens it against the steering shaft, is disclosed in EP 1 138 575 B1. The steering spindle part, on the end of which the steering wheel is secured, is here solid, however, it could also be formed as a hollow shaft with a sufficiently great wall thickness.
A further securement of a steering wheel at the end of the steering spindle part adjoining the steering wheel is disclosed in U.S. Pat. No. 4,819,961 A. The steering spindle part formed as a hollow shaft exhibits at its end a connection section in which the tube of the steering spindle part initially conically tapers toward its end and adjoining thereon comprises a hollow-cylindrical section with an inner toothing. In the connection section is disposed a clamping piece, whose outer contour corresponds to the inner contour of the tube and which projects from the tube at its end. It comprises first and second outer toothings, which, on the one hand, cooperate with the inner toothing of the tube and, on the other hand, with an inner toothing of the steering wheel hub. It exhibits, furthermore, an inner threading, into which a bolt is screwed engaging on the steering wheel hub in order to tighten the parts with one another. Through the solid clamping piece set into the connection section the wall thickness of the steering spindle part can be constant over its length. In such a clamping connection there is the risk that the applied clamping forces decrease over time whereby undesirable play may develop. The clamping piece must furthermore be inserted through the steering spindle part from the side remote from the steering wheel. Consequently, the steering spindle part must not have any regions with decreased cross section, for example in order to implement a telescopable torque-transferring connection with a further steering spindle part. The clamping piece, moreover, can slide into the interior of the steering spindle part when the steering wheel is removed, which consequently makes it inaccessible.
A steering spindle part according to the prior art will first be explained with reference to FIG. 1. This part is the rearmost, in reference to the traveling direction, steering spindle part of a steering spindle for a motor vehicle, on the end of which a steering wheel is to be attached. The steering spindle part comprises for this purpose a connection section 1 at the end facing the steering wheel. Starting from the end of the steering spindle part, this connection section 1 includes a hollow-cylindrical section 2 in which are formed an inner threading 3 and an outer toothing 6, and adjoining thereon toward the middle of the steering spindle part a conically widening section 4. In particular in the hollow-cylindrical section 2 the wall thickness D is greater than the wall thickness d in a section 5 adjoining the connection section 1 of the steering spindle part.
For the connection of the (not shown) steering wheel with the steering spindle part, the steering wheel is slid onto the connection section 1, wherein it comes to lie in contact with a conical inner wall on the conical section 4 and meshes with an inner toothing into the outer toothing 6. Furthermore, by means of a bolt threaded into the inner threading 3, the steering wheel is screwed down with the steering spindle part.
On the side remote from the connection section 1, the steering spindle part comprises a section 7 in which it is provided with a contour differing from a circular arc in order to form a connection, displaceable (telescopable) in the longitudinal direction of the steering spindle part, yet torque transferring, with a further steering spindle part. The section 7 can be formed in particular with a circumferential arcuate toothing or a cloverleaf profile.
For the production of this steering spindle part a tube is utilized as the starting product, which has a diameter and a wall thickness in the region of the section 5 which corresponds to the wall thickness D in the connection section 1. This initial wall thickness is at least greater than the wall thickness d in section 5, which is still adequate for the transfer of the torque since otherwise in connection section 1 a sufficient wall thickness cannot be formed. This tube is consequently worked using reshaping processes for the production of the steering spindle section, in particular by hammering and/or ductile-working, over its entire longitudinal dimension. If the tube in sections 5 and 7 were to be left in its original wall thickness, it would lead to a considerably increased requirement of material and accordingly to a large weight of the steering spindle part.